STEVEN R. BAGLEY INTRODUCTION TO THE COMPUTER

Transcription

1 STEVEN R. BAGLEY INTRODUCTION TO THE COMPUTER

2 INTRODUCTION Look at how a simple computer is built What are the main building blocks, how are they fitted together? Going to go fast, but will come back to all these concepts again in later lectures

3 How do we build a computer?

4 ABSTRACTIONS At this level, the abstractions leak a lot Digital Logic likes to think about signals switching between on, or off But in reality the electronics underneath don t behave like that C C standard Library Machine Code Operating System CPU Hardware Digital Logic Transistors Electronics Physics

5 CENTRAL PROCESSING UNIT The bit that does the actual computation Executes the instructions one by one In order implies time CPU needs to be driven by a clock

6 CLOCK Heartbeat of the system Everything the CPU does is sync d to this clock pulse This is what is meant when we talk about having a 2GHz CPU Doesn t necessarily specify how fast it is CPU might take more than one clock cycle to do something

7 CENTRAL PROCESSING UNIT CPU needs instructions to execute and data to operate on Represented as binary numbers Need to be fetched/stored from somewhere From Memory von Neumann model shared memory for program and data

8 DATA BUS Fetched from memory to CPU over the data bus Usually fetches more than one bit at a time 8-bit, 16-bit, 32-bits Not necessarily related to whether a CPU is 8-bit, 16-bit, 32-bit, 64-bit etc Bidirectional depending on whether the computer is reading or writing Micro Live clip 07:50 in Instrument our data bus see what s travelling over it

9 MEMORY Data bus allows one chunk of data to be transferred But computer needs to be able to access lots of data Each piece of data given a unique binary number, or address CPU specifies which bit of data it wants by providing the address on the address bus Read from this location, Write to that location Think of it like addresses of houses

10 ADDRESS BUS Carries the address for the piece of memory the computer wants to access In binary The number of address bus lines specifies how much memory the CPU can access

11 MEMORY Two types RAM Random Access memory ROM Read-only memory

12 RANDOM ACCESS MEMORY Can access any bit of data we like By providing the address Read/Write access Volatile wiped when the power is lost How do we get our program into it?

13 READ-ONLY MEMORY Again random access to any bit Can only be read Either pre-built with the values in place Or can get programmable ROMs that can be programmed with a special programmer Problem can t be modified

14 MEMORY How do we get the instructions into the computer? If we just have ROM, the program can t store any values If we just have RAM, there s no program Could build some extra hardware to let us program the initial instructions in first Solution: Have both ROM and RAM

15 ADDRESS DECODING CPU only has one address bus and one data How do we fit both ROM and RAM in? Connect the data bus to both the ROM and RAM But make sure only device is talking/listening to it at a time ROM and RAM have Chip select lines to enable or disable them By saying certain parts of the memory addresses refer to ROM or RAM (but not both) Called Address Decoding

16 CONTROL BUS What about the other wires Carry control signals that tell the rest of the system what the CPU is doing Read/Write is it reading or writing memory? Address Strobe Is the address bus valid? Data Strobe is the data bus valid?

17 I/O Input and Output depends on the processor Here we are using memory mapped I/O I/O devices appear as normal memory locations, so we just write data there Decode the Address to enable the relevant I/O thing Some CPUs have a separate I/O address space (e.g. x86)

18 Atari MegaSTe Block Diagram Address Bus Modulator RF Out Motorola MC /16 MHz Data Bus Atari GST Video Shifter Video to Monitor uwire Control DMA Sound Data Cache RAM Memory Data Atari Blitter Light Gun & Paddles Configuration & Controllers Atari GST Memory Control Unit (GSTMCU) Atari DMAC Mux'ed Address SIMMs ACSI Hard Disk 256 KB ROM 1772 FDC Int. Floppy Ext. Floppy uwire Control Joystick & Mouse Real-Time Clock DMA Sound Data 2149 PSG Stereo DACs Jacks Filters Mixer Audio Volume To Monotor Parallel Printer Port Floppy Drive Selects & RS-232 Control Keyboard 6850 Atari TTSCU VME Bus Keyboard MIDI Jacks MIDI MFP MFP to TTSCU Interrupts Serial Port Interrupts In MC68881/ LAN Port Optional RS-232 Port A Coproc SCC RS-232 Port B Block diagram of a computer