Overview of PC Systems

PC Systems

History

In the 1970s a new breed of computer appeared: the microcomputer.  Unlike mainframes and minicomputers a microcomputer could fit on a desk and was within the price range of small businesses and hobbyists.  By 1981 the microcomputer market had blossomed and home computers like the Sinclair ZX81, TRS-80 and VIC-20 were available in high street shops.

Small businesses were starting to see the advantage of microcomputers: in particular, the Apple II was selling well, with its groundbreaking VisiCalc spreadsheet software.  IBM, who dominated sales of large computers, decided to get in on the act and developed the Personal Computer (PC), aimed at business and home use.

The original PC was built around a 4.7 MHz Intel 8088 processor.  It could be fitted with up to 256KB of RAM and used a cassette tape for data storage (or optional 5¼" floppy disk drives).  The PC XT introduced in 1983 featured a 10 MB hard drive.

1984's PC-AT switched to the improved 80286 processor.  Many of the specifications of the AT still influence modern PC design, from drive measurements to keyboard layout.

Desktop PCs

A PC system includes all the parts needed to make a functioning computer:

• Input devices — keyboard & mouse
• Computer — system unit
• Output devices — display screen & printer
• Storage — hard disk drive, CD / DVD drive

Most PCs are constructed in a modular fashion, allowing parts to be exchanged or added to customise the system.

The system unit, also called the base unit or (inaccurately) the CPU, lies at the heart of a PC system.  The parts that plug into it, such as display screen or printer, are called peripherals.

System unit cases follow standard designs, allowing the use of modules from a range of manufacturers.  Component mounting holes and ventilation also follow common specifications.

Desktops sit horizontally on the desk and include thinner, low-profile, cases that have limited expandability.

Tower cases stand tall and often have extra space for further drive units.  Although they take up less desk space they have poor ventilation characteristics because air is heated by expansion cards before it reaches the processor.  To compensate, many towers use extra cooling fans.

Portable Systems

Portable PCs have always been popular, from the early suitcase-shaped luggables to laptops to modern PDAs.

Laptops (or notebooks, as modern lighter models are known) feature custom-designed motherboards.  They have a large rechargeable battery but may run from an external power supply.

Modern Tablet PCs feature flip-over displays and offer the ability to directly interact with the screen using a stylus.  Many feature advanced handwriting recognition to aid input.  Despite their convenience they have not yet replaced the laptop.  A half-sized version, the Ultra-Mobile PC (UMPC), was launched in 2006.  Both types run normal Windows.

PDAs (Personal Digital Assistant) offer many of the features of a modern PC in a handheld design.  Older assistants were glorified electronic diaries but the latest models offer web browsing, movie players, office applications, games, GPS navigation and dual functionality as mobile phones.

There are two primary operating systems used on these at present: Windows Mobile (formerly PocketPC or CE) and Palm OS.  PDAs may communicate with other machines through docking stations, infrared or wireless links.

Servers

Services

A typical modern operating system runs many programs that monitor performance, process messages going in and out of the computer, and communicate with other computers.  These programs are generally known as services and the commonly run continuously in the background.

A PC can provide very important services that respond to other computers across a network.

• File server — managing central storage of files for users on a network
• Print server — spooling (queuing) print jobs for network printers
• Web server — handing out webpages as they are requested by (client) browsers
• Email server — storing, sending & collecting email
• FTP server — managing storage of files via the Internet
• Database server — managing a large database for multi-user access
• Domain control server — handling central security for a network
• DHCP server — handing out IP addresses to computers on a network
• Proxy server — accessing the Internet on behalf of other computers

One computer could run many services.  However, in practice, it is often preferable to dedicate a separate computer for each service, free from interference by users’ applications or utilities.  Hence the dedicated computer is (also) referred to as a server.

File and database servers need a large amount of storage capacity.  In addition, domain controllers and proxy servers usually require fast processing.  Therefore most dedicated server computers are high-end, top-of-the-range machines.

RAID server

RAID servers are file servers with a large array of disk drives to allow fast, fault-tolerant file storage.  Their drives are typically hot-swappable and they include a RAID controller to manage distribution of data across the drives.  Many RAID servers include redundant (hot-swappable) power supplies and many fans to aid ventilation.

If you’re storing terabytes of important data you’ll need big backup facilities.  Tape backup and online backup is big business, and many companies have automated or live backup to offsite premises in case of disaster.

File servers can also be the building blocks of a SAN (storage area network) or NAS (network attached storage) server farms.

Blade server

A blade server contains several PC motherboards, each home to one (or more) processors, memory, storage, etc. — essentially a small network of computers in a single box.

Each motherboard is housed in a hot-swappable blade.  All blades share the same cooling system and a common (redundant) power supply, providing electricity more efficiently and reliably than separate supplies might.

Blades are usually proprietary to the manufacturer and cannot be swapped between different chassis types.