CPU (Cache), main memory, external memory;
Main memory: the main storage of instructions and data currently used CPU.
Characteristics: capable of random access, work fast, have sufficient storage capacity;
Secondary memory (external memory): store a large number of programs and data backup.
Features: slower, larger capacity;
Cache: storing CPU programs and data used in the current multiple short period of time, the CPU and main memory to alleviate the difference in speed.
Features: very fast, small volume;
Physical memory and virtual memory:
Physical memory: the memory real physical form, referred to as real storage, which is called the physical address or addresses real address.
Virtual Memory: Virtual memory is a logical model, not a physical presence, and by hardware + operating system based on physical memory mapping to implement.
Classification memory (in storage medium):
The semiconductor memory:
Static memory: storing information using two stable states of the flip-flop, a volatile information;
Dynamic memory: depend on charge on the capacitor temporary information, the main memory.
Magnetic surface of the memory:
Using different directions of magnetic layers magnetized region information indicates, large capacity,
CD-ROM memory:
Presence or absence of light spot equal to / change information indicating the crystal, a large capacity, non-destructive readout, the information stored for a long, slow, external memory.
Classification memory (According to the way):
A random access memory (Random Access:, regardless of the address access time of the memory cell at the address in the memory access any cell);
Sequential access storage: Read access / write means in order to find the destination address, the access time of the storage location-related data;
The direct access storage: a read / write to a small region coarse positioning access, and then find the sequence in this region.
Memory Specifications:
Access time, the access cycle, data transfer rate;
Static RAM: relying on the memory cell formed interlocking cross feedback circuit, for storing information by continuously supply power to the circuit.
Dynamic RAM: rely gate capacitance formed in the storage unit to store information, does not require constant power, it needs to be periodically refreshed line by line.
Design principles memory:
Interface protocol matching (physical characteristics, the functional specification, level characteristics, the timing logic, etc.);
Selecting memory chip;
Address assignment and address decoder of the memory;
Chip layout and cable;
Dynamic memory refresh:
Refresh mean: replenished periodically charge the capacitor.
The reason: the charge storage capacitor dynamic memory to rely on information, not continuous power supply, the charge will leak, so the need to regularly replenish the charge capacitance in order to maintain the information stored unchanged.
The maximum refresh interval DDR: 64ms
Refresh method: Progressive refresh;
Refresh and rewrite the difference between:
Regardless of the read and write operations to refresh, automatic replenishment charge periodically to keep the information; automatic operation after rewriting is destructive readout, in order to restore the original information.
Refresh cycle arrangements:
Refresh centralized, decentralized refresh, refresh asynchronously;
Magnetic surface of the memory:
Storage medium and the head:
Storage media: magnetic material;
Reading and writing principles:
Two kinds of mode of magnetization: horizontal magnetization \ perpendicular magnetization;
Storage media: magnetic layer;
Read / write means: a head;
Data is written: magnetic head coil added magnetizing current (write current), the mobile magnetic layer, magnetization of small pieces forming a continuous zone (zone bit cell).
Read out: without the coil current, magnetic movement. When the bit cell transition region passes underneath the head, across the coil induced voltage is generated.
Magnetic encoding:
Use some variation of the sequence into a string of binary code corresponding to the record layer in the magnetization state.
Centralized common recording:
NRZ system -1 (NRZ 1)
Phase modulation system (phase modulator PM, phase encoding PE)
Frequency Modulation (FM)
Modified Frequency Modulation (MFM or M ^ 2F)
Group code system (the GCR)
Disk memory and its interface:
Disk system includes the following sections:
Hardware: a disk (bank), a magnetic disk drive, the disk controller interface.
Software: The main program is a hard disk drive, fixed in ROM.
Hard disk: for calling more frequent occasions, often as a direct backup of main memory.
Disk: single or double record;
Group plate: a plurality of discs assembled into a disk pack;
Whole column disk (RAID): forming a plurality of disk groups;
Hard disk information distribution and addressing information:
Information Distribution:
Group plate: a plurality of discs, two-sided recording;
Cylindrical surface: the same track number of each recording surface constituting a cylindrical surface (cylindrical surface = channel number / surface)
Data block: a sector (fixed-length record format); recording block (variable-length record format), no sectorized;
Addressing modes:
--- the drive letter head number cylindrical surface --- --- No --- sector number byte sequence number;
Determining determines hard cylindrical surface determines the positioning of magnetic sectors Byte
Recording format (track format):
Unformatted capacity
Disk track number = Number × / × inner surface of the inner circumferential length × dislocation density;
Formatted Capacity
× disk track number = Number / area × number of sectors / channels × number of bytes / sector;
The basic operation of the hard disk:
Addressing Data: Looking track (radial movement of the head) ---- Looking sector (disk rotation)
Write data: a serial read / write format conversion ---- ---- input / output (DMA)
Technical indicators and check the hard disk
Recording density:
Track density: the number of tracks the disk radially inside the unit length;
Bit density: the number of bits per unit length of tracks can be recorded;
storage capacity:
Formatted Capacity: calculated by a sector;
Unformatted capacity: the bit density is calculated by;
Speed indicators:
Average access time (seek + rotation), the data transfer rate (bandwidth);
Verification of the magnetic surface of the memory
Hamming check
Cyclic Redundancy Check (CRC)
Disk Adapter
Function and role:
Bus for: providing a bus interface logic meet the criteria;
For a magnetic disk drive: providing a disk drive interface logic matching;
Industry Standard:
SCSI, IDE, SATA 等
Optical memory
Optical storage principle:
Storage medium is irradiated with a laser, so that changes in certain physicochemical properties occurs, whereby information is recorded.
Storage medium characteristics: deformation type, phase change type, magnetooptical type;
Laser wavelength and focal length;
CD-ROM memory:
Track wherein: each track is also divided into a plurality of sectors; spiral from the inside out, and the structure is similar to mosquito coils.
Set the Cache reasons:
To solve the CPU and main memory speed mismatch and a technique employed, the average velocity close to the speed of main memory access to the Cache. Hardware system implementation, transparent to the user. Has been integrated in the CPU, more than two Cache system.