2015年12月11日
"It took me a year to understand
That, said Mr Barr, left the Edsac reconstruction project with a big problem. Namely, they did not have a clear idea of how the thing was wired up.
The project to recreate Edsac was undertaken to help fill gaps in knowledge about the way that this early British computer was built and worked. Once complete it will become a living exhibit at The National Museum of Computing where it will be used to help teach schoolchildren about programming.
The early months of the reconstruction scheme were taken up studying photographs of the finished computer to try to work out how its 3,000 valves were laid out and how they formed the logic that lent the machine its computational power.
Latterly, some plans for Edsac were discovered and have helped the builders confirm they were heading in the right direction. However, said Mr Barr, they turned up long after the heavy mental work had been done to understand the machine.
Image copyright The Edsac Project
Image caption James Barr has toiled in his shed to get the Edsac chassis working
"It took me a year to understand its five-bit order code," said Mr Barr. But understand it he did and his insights, along with those from fellow engineers who have worked on other key parts of the machine, has helped the project recreate Edsac's innards.
Which is where the sheds come in.
Those logical parts are being turned into hardware, known as chassis, in sheds and attics up and down the country. This has involved huge amounts of work as Edsac is built of 140 chassis spread around a series of tall racks. Each one is about 80cm long by 60cm wide, studded with valve sockets and stands in front of a spider's dream of wiring.
The project to recreate Edsac was undertaken to help fill gaps in knowledge about the way that this early British computer was built and worked. Once complete it will become a living exhibit at The National Museum of Computing where it will be used to help teach schoolchildren about programming.
The early months of the reconstruction scheme were taken up studying photographs of the finished computer to try to work out how its 3,000 valves were laid out and how they formed the logic that lent the machine its computational power.
Latterly, some plans for Edsac were discovered and have helped the builders confirm they were heading in the right direction. However, said Mr Barr, they turned up long after the heavy mental work had been done to understand the machine.
Image copyright The Edsac Project
Image caption James Barr has toiled in his shed to get the Edsac chassis working
"It took me a year to understand its five-bit order code," said Mr Barr. But understand it he did and his insights, along with those from fellow engineers who have worked on other key parts of the machine, has helped the project recreate Edsac's innards.
Which is where the sheds come in.
Those logical parts are being turned into hardware, known as chassis, in sheds and attics up and down the country. This has involved huge amounts of work as Edsac is built of 140 chassis spread around a series of tall racks. Each one is about 80cm long by 60cm wide, studded with valve sockets and stands in front of a spider's dream of wiring.
2013年02月19日
The ATSC standard
Digital television in the United States will be using the standard ATSC ( Advanced Television System Committee Advanced Television Systems Committee ), ATSC digital TV standard consists of four separate layers, with clear interface between levels. The highest as the image layer, determine the form of images, including pixel array, amplitude ratio and frame rate. Then the image compression layer, using MPEG-2 compression standard. Then system multiplexing layer, specific data can be incorporated into different compression package, using MPEG-2 compression standard. The last is the transport layer, determine the modulation and channel coding scheme of data transmission. For terrestrial broadcasting system, using the 8-VSB transport model developed by zenith, in 6mhz terrestrial broadcasting channel can realize the transmission rate of 19.3mb/s. This standard also contains is suitable for CATV system with high data rate 16-vsb transmission mode, can realize the transmission rate of 38.6mb/s in 6mhz cable TV channel.
The following two layers to share common data transmission. The above two layers determine the specific configuration operation based on common data transmission, such as HDTV or SDTV.
The above two layer also determine the specific image format supported by the ATSC standard, a total of 18 formats ( HDTV6, SDTV12 ), 14 of which employ progressive scanning.
A.HDTV, 1920 pixels ( H ) X1080 ( V ), pixel aspect ratio of 16:9, frame 60HZ/ interlaced, progressive scan frame 30Hz/, frame 24Hz/ line-by-line scanning system;
B.HDTV, 1280 pixels ( H ) X720 ( V ), pixel aspect ratio of 16:9, 60Hz and 30Hz frame rate, 24Hz/ line-by-line scanning system;
C.SDTV, 704 pixels ( H ) x480 ( V ), pixel aspect ratio of 16:9 or 4:3, a 60Hz/ interlaced scanning system, frame rate 60Hz and 30Hz, 24Hz/ line-by-line scanning system;
D.SDTV, 640 pixels ( H ) x480 ( V ), pixel aspect ratio of 4:3, a 60Hz/ interlaced scanning system, frame rate 60Hz, 30Hz, 24Hz/ line-by-line scanning system .
In addition, ATSC also develops through the frame rate of 50Hz countries use the prior standard. The pixel array HDTV the same, but the frame for the vertical resolution of the 25Hz and 50HzoSDTV format as 576 rows of horizontal resolution is different; also contains 352x288 format, necessary to adapt to the window settings. Based on the 50Hz version of the ATSCDTV standard to make the frame rate of 50Hz countries are more easy to use.
The following two layers to share common data transmission. The above two layers determine the specific configuration operation based on common data transmission, such as HDTV or SDTV.
The above two layer also determine the specific image format supported by the ATSC standard, a total of 18 formats ( HDTV6, SDTV12 ), 14 of which employ progressive scanning.
A.HDTV, 1920 pixels ( H ) X1080 ( V ), pixel aspect ratio of 16:9, frame 60HZ/ interlaced, progressive scan frame 30Hz/, frame 24Hz/ line-by-line scanning system;
B.HDTV, 1280 pixels ( H ) X720 ( V ), pixel aspect ratio of 16:9, 60Hz and 30Hz frame rate, 24Hz/ line-by-line scanning system;
C.SDTV, 704 pixels ( H ) x480 ( V ), pixel aspect ratio of 16:9 or 4:3, a 60Hz/ interlaced scanning system, frame rate 60Hz and 30Hz, 24Hz/ line-by-line scanning system;
D.SDTV, 640 pixels ( H ) x480 ( V ), pixel aspect ratio of 4:3, a 60Hz/ interlaced scanning system, frame rate 60Hz, 30Hz, 24Hz/ line-by-line scanning system .
In addition, ATSC also develops through the frame rate of 50Hz countries use the prior standard. The pixel array HDTV the same, but the frame for the vertical resolution of the 25Hz and 50HzoSDTV format as 576 rows of horizontal resolution is different; also contains 352x288 format, necessary to adapt to the window settings. Based on the 50Hz version of the ATSCDTV standard to make the frame rate of 50Hz countries are more easy to use.
