Most PCs with Windows XP originally came with 128 to 512 megabytes RAM. Recent models running Windows XP (netbooks, ULCPCs) typically have one to two gigabytes (One gigabyte = 1,024 megabytes).

Avoid Microsoft® Windows® Vista Home Basic

Dell and other OEMs are still selling low-end computers with Windows Vista Home Basic. Windows Vista Basic does not qualify for upgrade pricing to Windows 7 and will not be supported after April 2012. Instead, choose an upgrade to Windows 7 Home Premium which will be supported through January 2015.

Steer clear of single core processors (CPUs) for standard desktop computers

Computer manufacturers offer single core processors at the very low end. While single core can be satisfactory in a properly configured tablet computer or netbook, desktop computers should generally be equipped with dual core or greater. Dual core processors can better handle multiple tasks and are more responsive shortly after boot and when running antivirus scans. Additionally, some software imaging suites and AOL software can absolutely hog a single core CPU and render the computer temporarily unusable. Choosing a dual core processor can alleviate much of that load.

Single core processors include the Intel Celeron, Atom and the AMD Sempron and Athlon families. Models I specifically advise to avoid are the AMD Sempron LE series and the Intel Celeron 420 through 450. These are older technology processors (about three years old) sold with new basic desktop computers. Again, stay clear of these processors. Buy dual core instead.

Acceptable single core processors

Exceptions to the above include the AMD Semprons 140 and 145 and AMD Athlon 2850e and 2650e. The Sempron 140/145 are new 45 nanometer (45nm) technology models that actually perform quite well. The Athlons 2850e and 2650e, though older 65 nanometer models, outperform the Intel Atom. They have reduced core voltage for lower power consumption in special computers such as the Dell Zino HD.

With any single core processor, take extra care not to load too many applications that will cause startup delays. Additionally, choose a low impact security application such as the free Microsoft Security Essentials or ESET NOD32 Antivirus 4 for best results. Be sure to fully uninstall any other active security application before installing another.  

Recommended Desktop Processors: Intel Core i3-530/i3-540

The Intel Core i3-530/i3-540 dual core processors are a best buy for anyone seeking moderately high performance at a reasonable price. Both models outperform some quad-core CPUs in the majority of tasks. Dell, Gateway and Hewlett-Packard offer these processors online and in stores. I recommend the following desktop computer models for most users:

HP Tower Series p6370t base configuration

HP Slim Series s5370t base configuration

Dell offers the Core i3-530 with the Dell Inspiron 580 and 580s but pre-install more RAM in their base configuration (6 GB) than what is needed for most home users  (3 to 4 GB RAM is sufficient for the majority of us). The price of RAM has soared in the past six months with the global increase in demand. That has added significantly to the price of a computer.

Update: Use care with CPU upgrades. Upgrade only to another family. Do not pay for an upgrade from a Core i3-530 to an i3-540.

A solid option is the new Intel Pentium G6950 processor which is available at a lower cost with the Dell Inspiron 580 models and equivalent HP and Gateway systems. The Intel Pentium G series will supplant and eventually replace the previous generation Intel Pentium E in the marketplace during the next twelve to fifteen months.

Suggested HP Basic Desktop Computer with Windows 7

Hewlett-Packard's Pavilion p6310t desktop comes with 2 GB memory, a 320 GB hard disk drive and an Intel Celeron 450 single core processor for $349.99 (instant rebate of $100.00 applied) plus tax and shipping. I strongly advise upgrading to an Intel Celeron Dual Core E3300 processor for an additional $20.00. A memory upgrade to 4 GB is offered but at $80.00 is overpriced and is not necessary for a basic Windows 7 64-bit system.

Shoppers should note that when choosing an upgrade processor,  an internal clockspeed boost alone is usually overpriced and not worthwhile. The best upgrades will include a boost in the L2/L3 Cache specification. Such an increase in Cache usually occurs when upgrading from one family to another.

Purchasing desktop computers with single core processors is not recommended.

The oldest and least efficient technology in this table is the nearly three years old single core Celeron 400 series manufactured with 65 nanometer technology.

Note: This article is being revised and will soon incorporate a simplified table guide similar to the above desktop table.

Today's laptops are subdivided into four categories: netbook, ruggedized/specialized tablet, thin notebook and full-function laptop/notebook. To add confusion, processors are often similarly named to desktop models but are quite different in physical characteristics and performance.

Popular netbooks generally feature older under-clocked Intel Celeron M processors or newer Intel Atom family processors. The under-clocked Celeron M models are of an old micro-architecture and are being being phased out. Intel Atom processors perform about as well as five to seven years old Pentium M processors but use a fraction of the electric power. Low power consumption is is one reason netbooks can be made so small. Keep in mind that loading a netbook with heavy-duty security suites can noticeably impact responsiveness. For top performance from a netbook, keep it clean and lean.

Tablet computers are designed for doctors, utility meter readers and any professionals who need a tough and durable design. Most are used for a narrow range of applications requiring minimal processing power but a long-running reliable battery. Low-voltage single core CPUs work well with such systems once booted and security programs loaded.

Thin notebooks/laptops are similar to tablet models except for thin models lacking a tough case. Thin models are aimed at home and travelling users who want the smallest profile in a large size screen and the least amount of weight. Processors are generally single core ultra-low voltage models with an SU designation or from the Intel Atom family. Dual-core SU models are available and are worth the extra cost.

For full-size laptops, I strongly recommend choosing a dual core processor from the Intel Core i3 or i5 series as the laptop versions of these processors are exceptionally efficient and powerful. Optionally, the Pentium Dual Core or older technology Core 2 Duo models are acceptable at reduced prices.

For those who need the best in laptop performance, look at the quad-core Core i7 series from Intel. They are ideal for those using a laptop as a desktop replacement and doing video and audio editing and professional image manipulation. They also are great for advanced games. Expect prices of computers such as the Dell Precision M6500 or Alienware laptops to be high.

Single core Intel Celeron processors are satisfactory for basic applications but keep in mind that performance will be noticeably affected if using a security suite such as McAfee, Norton Internet Security, Verizon Security Suite or AOL software. Single core processors are not recommended for video editing or professional image manipulation.

The following table is being edited for accuracy. It will be completed later.

Microsoft® Windows® 7 Versions

Following are the Windows 7 versions released in the U.S:

Windows 7 Home Premium -(green case)- a comprehensive multimedia-centric product recommended for most consumers. Guaranteed mainstream support is standard through January 13, 2015. Extended support is not available.  

Windows 7 Professional -(blue case)- for businesses, students, and enthusiasts. This is a true superset with all of the features of Home Premium plus enhanced networking capabilities, file encryption and downloadable "XP Mode" for older productivity applications requiring Windows XP Professional in 2D display mode. (Note that XP Mode is not for 3D modeling or 3D games.) Windows 7 Professional will receive a total of at least ten years of security update support. It is the best choice if planning to keep a new computer and operating system for the long term.

Windows 7 Ultimate -(black case)- This version is the same as Windows 7 Professional except for the addition of more advanced encryption capabilities and multi-language switching. Extended support is not available. Persons not needing multi-language capability on the fly but desiring advanced networking features and long-term security update support should choose Windows 7 Professional.

Windows 7 Starter - for Ultra Low-Cost PCs including netbooks. This restricted OEM 32-bit-only version is offered globally without the full feature sets of Home Premium or Professional. Extended support is not available. Windows 7 Starter is not expected to be popular due to certain features being disabled.

Windows 7 Enterprise - for medium to large businesses. Enterprise is Windows 7 Ultimate with volume licensing plus extended support. It is not available for retail sale to individuals.

For detailed information about the new versions visit Paul Thurrott's Windows 7 Product Editions: A Comparison.

Windows Vista Home Basic is not a good upgrade candidate

Upgrading from Windows Vista to Windows 7...

...is a far smoother process than what many experienced upgrading from Windows XP or earlier to Windows Vista. That is because Windows 7 is based upon the Windows Vista SP1 kernel (core operating system files) and the file hierarchy is similar. Additionally, most Windows Vista systems have at least one gigabyte of RAM and are compliant with system requirements. So the upgrade process should be relatively quick and easy. For users not confident in transferring their files, Microsoft has indicated that data transfer tools will be available to assist with Windows 7 post-installation setup.

Upgrading from Windows XP to Windows 7...

...is not as easy as upgrading from Windows Vista. A clean install is required; that is, personal data must be backed up to external media and the hard disk drive must be wiped clean prior to installing Windows 7. Data is then copied from the backup source. Programs will have to be installed from scratch and updated.

A major concern regarding Windows XP systems; many are simply too old and expensive to upgrade. That is especially true of early Windows XP systems with less than one GB RAM.

When considering upgrading an older computer to Windows 7, shoppers should be aware that a new desktop computer that can run Windows 7 satisfactorily can be purchased for less than $500.00. Therefore, buying a new computer may be more cost and time-effective than upgrading an old system from 2006 and earlier. In contrast, computers built in 2007 and later with at least one gigabyte RAM should be able to run Windows 7 quite well.

Resources: How to Upgrade to Windows 7

How to Upgrade to Windows 7 from MSNBC Tech.

Detailed steps from Microsoft Corporation with video tutorial: Upgrading from Windows XP to Windows 7.