Desktop PCs take on the tablets Last week I wrote about the new iPad, which Apple sees as the poster child of a post-PC world. Can the PC fight back? New contenders from the leading manufacturers - Hewlett-Packard, Lenovo and Dell - are staking their claims. Omni 27 (4/5) The desktop PC may not be as mobile as a smartphone or a tablet, but it certainly seems to get around the house more these days. I have been trying HP's Omni 27 all-in-one computer on the kitchen counter and in a bedroom, while Lenovo's new Q180 mini-PC and Dell's Alienware X51 gaming machine have been put to work with our living room television, as well as the desk in my home office. The modern PC needs to be something of a shape-shifter to remain relevant and to compete head-on with smart TVs, tablets and the other devices that are starting to match its powers. It also helps if the PC looks more appealing than the upright box with whining fan we all know. HP's Omni 27 is like a tablet or a smart TV in terms of it being all about the screen - the usual PC innards are hidden within the smooth back of the monitor. On sale from $1,200 (£1,000), it certainly looks good, with its elegant stand and edge-to-edge, 27in glass monitor. Built-in WiFi and a well-made wireless keyboard and mouse mean there is a welcome absence of wires - apart from the power cable. Anything required for connectivity is hidden away, including seven USB ports, memory card slot, ethernet and HDMI ports. The HDMI connection is useful for linking up a games console to use the Omni 27 as just a monitor. There is an optical drive and an excellent high-definition webcam built in; HP Beats speakers provide good audio for their size; and I enjoyed listening to and watching a movie on the 1080p HD screen. The screen is not a touchscreen as HP is aiming to provide an affordable alternative to Apple's 27in iMac - a non-touch all-in-one. Apple's machine has a higher-resolution screen but the Omni 27"s sound is better, it has twice the memory (8Gb) and is less expensive ($330 cheaper in the US) than a comparable iMac. IdeaCentre Q180 (3/5) Lenovo plans to provide an interesting all-in-one alternative shortly with its A720, in which the main feature will be the affordable addition of touch to a 27in screen. In the meantime, the company is doing its best to make the desktop disappear in a different way from the all-in-one approach with its IdeaCentre Q180, "the world's smallest desktop PC." The tiny box, similar in size to a Mac mini, is less than 1in thick, but has all the connectivity - USB ports, memory card slots, HDMI - you would expect in a PC. It has an innovative remote that is ideal for typing from the couch, but it otherwise seemed odd to have a PC, however small, with trailing keyboard and mouse wires plugged into my 55in television as recommended. The Q180 (from $379, £400) seems more suited to a bedroom or desk where space is at a premium - an optional mounting bracket will fix it to the back of an existing monitor to make a do-it-yourself all-in-one. Alienware X51 (3/5) Like the Lenovo, the X51 from Dell's Alienware gaming PC division is designed to sit under a TV and is as whisper-quiet as the HP and Lenovo machines in operation. While it can lie horizontally and easily compete in performance terms with the ageing Xbox 360 or PlayStation 3 in the TV cabinet, it looks more impressive when stood vertically with its side-panel lighting accents. When I played PC games they had just as good resolution and high frame-rates as on a dedicated console. With prices starting at $699 (£649), this is the most moderately priced and compact gaming PC yet produced by Alienware. Overall, the game is clearly not up for PCs if HP, Lenovo and Dell can continue to innovate in these ways.