A diagnostic test should be carried out in addition to the general test, to ensure that nothing has been overlooked. These tests will be carried out using diagnostic routines supplied by the manufacturer of the machine or by a third party. Several third party diagnostic programs have been written for the PC, the most popular being Norton Utilities, Checkit and PC-Check These will test the following areas:

• The Memory - Several tests will be run on the memory to check that it can write and read data correctly. For a PC this will generally divide the memory into two, the base memory (any memory up to 640KB) and the extended memory (the area of memory above 1MB). Some will check external cache memory as well. They will carry out different types of tests such random, walking "1"s and checker-board patterns, which place the data in the memory in such a way as to check it thoroughly.
• The Input/Output ports - These tests will check the serial and parallel ports of the machine and will normally require a Wrap-plug, sometimes called a Loop-back plug, which is a plug wired in such a way that the output pins are wrapped around to the input pins (simulating normal use). The wrap-plug may be supplied with the software or a diagram will be supplied that will enable the IT Systems Support Technician to make one up. The tests carried out will include checking the handshake signals, generation of interrupts, controller, individual pins and external loop-back. The software will usually display the interrupts being used.
•  Floppy Disc - This will generally need a scratch floppy disc so that data can be written to it. There will be non-destructive read and write tests and the diagnostic routines will be run on the controller. Some diagnostic programs can check up to two units at the same time, as long as they are fitted into the same machine.
• Hard Disc - Similar diagnostic routines are carried out to those of the floppy disc. The routines would include non-destructive read and write tests, normal read and write tests and controller diagnostics. They will also include low-level format routines and configuration for SMART 1. On some programs up to four hard disc units can be tested at the same time.
• Motherboard - There will be checks for the DMA Controller, System Timers, Real-Time clock, Interrupt Controller, Keyboard Controller and the PCI bus. There will also be routines for checking and setting the CMOS settings.
• Processor and co-processor - Tests include identification, monitoring the frequency and the step-speed.
• Keyboard - Tests for functionality, scan codes, LEDs and key operations.
• Mouse - This test will usually test the operation of the mouse and its buttons in both text and graphics modes.
• Video Adapter - This will usually include tests for monitor alignment and linearity, the colour palettes and video memory. Some programs have support for AGP and can generate Test Cards.
• Other hardware items - Some diagnostic programs will also check peripherals such as LS-120, ZIP drives and the USB controller.

Some of the diagnostic programs, Norton Utilities for example, include disk editors and disk repairers. Some operating systems will also include programs to repair disks such as SCANDISK.EXE, DEFRAG.EXE or FSCK. Most of the diagnostic programs will include the retrieval of system information such as: 

• Processor type and speed 
• Co-processor identification 
• BIOS signature and release date 
• DOS release version 
• Bus identification 
• Interrupt use, value and vectors 
• How the memory is being used 
• Which multimedia devices are installed 

Other utilities may include: 

• Routines for checking the modem 
• Saving and restoring the Disk boot block 
• SCSI utilities for device identification and low-level format 
• The diagnostic routines should not be used in isolation - they are only fully effective when used with other diagnostic aids, such as the POST error codes and beeps, test measurements, and information from system users. 
  
  [1] SMART - Self-Monitoring Analysis and Reporting Technology. This is technology that allows the hard disc to monitor itself and report on problems found. This is usually enabled in the CMOS settings.