System Bus

1. System Bus

2. XT Mother-boards “extended technology.” Configured manually using jumpers, switches or both. Designed around the Intel 8088 processor. Has an eight-bit ISA bus Limited to 1MB of memory

3. System Bus • The heart of any motherboard are the various buses that carry signals between the components. • The PC has a hierarchy of different buses ordered by their speed. AGP System bus Processor System bus • Each device in the system is connected to a bus ISA System bus PCI System bus

4. Processor System Bus Processor System Bus is also called the front side bus Primarily used by the processor to pass information to and from cache, main memory and the North bridge It is the highest speed bus

5. AGP System Bus AGP System Bus is a high speed 32 bit bus Primarily used for video and is connected to the North bridge Only one AGP bus per system

6. PCI System Bus PCI System Bus is normally a 32 bit bus • Primarily used by all newer 486 and higher processor systems

7. ISA System Bus ISA System Bus is a very slow speed 8 Mhz, 16 bit bus The Super I/O chip usually was connected to the ISA Bus ISA Bus is generated by the South Bridge, which acts as the controller and interface between the ISA Bus and the faster PCI Bus Most new motherboards no longer support ISA

8. Expansion I/O Buses Standardized Connectors on the motherboard This is where peripheral devices are attached ISA AGP PCI MCA VESA PCMCIA/PC Card EISA Allows for exceptional flexibility Processor speed bottleneck

9. ISA (Industry Standard Architecture 8/16-bit ) 8 bit ISA Card 16 bit ISA Card Originally ran at 4.77 MHz with 8 bit cards Supports 16 bit slots while staying backward compatible with 8 bit cards With 16 bit cards ran at 6 MHz, then 8 MHz, then finally standardized at 8.33 MHz Black in Color

10. MCA (Microchannel Architecture16/32-bit) Introduced by IBM Not compatible with ISA cards May be 16 bit or 32 bit depending on the card 32 bit MCA Card Brown in Color Supports bus mastering. This can control the bus and act as if it were the entire systems

11. EISA (Extended Industry Standard Architecture 32-bit) Created by Compaq, so they would not have to pay royalties to IBM 32 bit throughput with an automated setup Supported bus mastering and would work with 16 bit ISA cards 32 bit EISA Card Brown in Color/ Two levels

12. VESA (Video Electronics Standards Association 32-bit Local Bus) Limited to 3 cards Referred to as VL bus (VESA local bus) Direct access to Processor Bus, therefore direct access to system memory for higher speeds than others Faded into history because of speed issues, but was resurrected as AGP 32 bit VESA Card Completely different physical makeup to prevent plugging in slower cards Brown in Color

13. PCI (Peripheral Component Interconnect 32/64 bit Local) • Developed in 1992 to solve the problem of fast CPU’s • Transfers data at 33 MHZ at full data width • Operates at same time as the CPU without replacing it 32 Bit PCI Card White in Color

14. PC Card (PCMCIA) • Introduced in 1990 to give laptop and notebook computers expansion capabilities • 4 standard types • Type 1 : 3.3mm • Type 2 : 5mm • Type 3 : 10.5mm • Type 4 : 10.5mm & up • Included in the PnP (plug and play) specification • Introduced concept of combining the device and its I/O card on the card

15. Accelerated Graphic Port • One of the main reasons Intel designed the AGP was to allow the video card to have a high speed connection directly to the system ram • The AGP was created in 1996 as a bus specifically designed for high performance graphics and video support • AGP is a high speed connection and runs at a base frequency of 66 MHZ which is double that of a standard PCI • AGP is based on PCI, but it contains additions and enhancements and is physically, electronically, and logically independent of the PCI